1. Field of the Invention
The present invention relates to a storage system comprising a plurality of storage devices.
2. Description of the Related Art
An information system is generally equipped with a storage system using a HDD (Hard Disk Drive) as a storage device, and such storage system is accessed from a plurality of higher-level devices (for example, hosts) via a storage area network (SAN). Storage control in the storage system is conduced according to a RAID (Redundant Array of Independent (or Inexpensive)) technology. As a result, a highly reliable information system can be realized.
On the other hand, since the bit cost of flash memories has been decreasing in recent years, flash memories have become effective storage devices. Japanese Patent No. 3507132 discloses measures against write failure caused by the increase in the number of rewrite cycles, which is a drawback of flash memory.
A storage system can be considered in which a flash memory is installed instead of or in addition to a HDD and data that will be read out or written into a higher-level device are stored in the flash memory. It can be anticipated that a storage system having the same storage capacity as a storage system based on a plurality of HDD will be realized by providing a large number of flash memories.
Though Japanese Patent No. 3507132 discloses measures against the increase in the number of rewrite cycles, which is a drawback of flash memory, no measures against a signal component failure (blockage) is disclosed. Such a measure being absent, data stored in a flash memory can be volatilized by a single component failure and, therefore, reliability of storage system cannot be increased even if a storage system comprising a plurality of flash memories can be increased in capacity.